Nu Sigma Nu is a medical fraternity founded in 1881 at the University of Michigan.

http://www.umich.edu/~nusigman/

Nu Sigma Nu was founded on the 2nd of March in 1881 right here at the University of Michigan, making it the oldest medical fraternity in the nation. The founding members were Robert Stephens, Charles Frye, Benjamin Strong, Fred Main, John Gish, and William Mayo, founder of the Mayo Clinic. In fact, legend has it that our billiards here in the house once belonged to Dr. Mayo himself.